It's entirely possible to go into QGIS and just start doodling. In my experience, the big value in software like QGIS isn't necessarily the drafting aspect, but being able to do relational analysis (How many trees are within ten feet of a road? Which towns are more than three miles from a river? How many Starbucks should be placed on one intersection based on the per capita density of plaid shirt distributors in the local area?). I doubt you're interested in this kind of information.

Also, since you're asking about fantasy realms, a lot of the first steps are kind of irrelevant. For example, in the real world, I would say that you should check your projection as a jumping off point. However, unless you really love your fantasy world, I doubt you have projections for it.

In short, go nuts. Fire up GQIS and play around. You're not creating migratory data, so it doesn't really matter what you do. You could probably just take a sample data set and clear it out for a brand new sandbox. I'm honestly not sure how much this will help you learn real GIS skills, though.